Spatial behavior: the impact of global and local geometry.

Humans and other animals use the global geometry of the surrounding environment in order to orient and determine which direction they are facing. Accordingly, the impact of environment geometry on spatial behavior is reflected in the paths of progression in the environment. When the perception of the global geometry is limited, such as in large or dark environments, the global geometry of the environment has to be constructed gradually as the accumulated geometry of locales. In the present study, we progressively altered the form of a dark square test arena by means of local alterations to its corners and walls, in order to differentiate the impact of the global arena geometry from that of the local arena geometry sectors on spatial behavior in rats. We found that as long as the local alterations did not distort the global square geometry of the dark environment, the rats' behavior did not significantly change. In contrast, distortion of the square shape of the arena resulted in significant changes in the spatial distribution of the rats' activity. Accordingly, we suggest that the perceived global geometry affects spatial behavior, overriding the impact of the local geometry.

City rats: insight from rat spatial behavior into human cognition in urban environments.

The structure and shape of the urban environment influence our ability to find our way about in the city. Understanding how the physical properties of the environment affect spatial behavior and cognition is therefore a necessity. However, there are inherent difficulties in empirically studying complex and large-scale urban environments. These include the need to isolate the impact of specific urban features and to acquire data on the physical activity of individuals. In the present study, we attempted to overcome the above obstacles and examine the relation between urban environments and spatial cognition by testing the spatial behavior of rats. This idea originated from the resemblance in the operative brain functions and in the mechanisms and strategies employed by humans and other animals when acquiring spatial information and establishing an internal representation, as revealed in past studies. Accordingly, we tested rats in arenas that simulated a grid urban layout (e.g. Manhattan streets) and an irregular urban layout (e.g. Jerusalem streets). We found that in the grid layout, rat movement was more structured and extended over a greater area compared with their restricted movement in the irregular layout. These movement patterns recall those of humans in respective urban environments, illustrating that the structure and shape of the environment affect spatial behavior similarly in humans and rats. Overall, testing rats in environments that simulate facets of urban environments can provide new insights into human spatial cognition in urban environments.

How do global and local geometries shape exploratory behavior in rats?

The present study examines how rats process object information in relation to other objects as well as to the global shape of an enclosure. Rats were introduced into either a round or a square arena with various arrays of freestanding portable corners (objects) that differed in spacing, orientation, and number. We found that the time spent at the objects was substantially higher in the round compared with the square arena. Rats in the square arena distributed their time evenly between arena perimeter and objects; however, they visited the objects more frequently than the perimeter. Rats tested in either round or square arena favored staying at the interior of the object regardless of its orientation in the arena. Finally, only geometric changes in the object array affected the rats' level of activity. These findings demonstrate that the rats were able to detect the geometry of the enclosure, the array, and the objects. We suggest that the context of the global enclosure geometry affects the meaning of landmarks (objects) for the observer, which in turn results in a different distribution of activity. Specifically, an object's local geometry served mainly in the context of a safe place in the round arena, as manifested in extended duration of stay at the objects, however in the square arena served mainly as a place of interest, as manifested in the frequent visits, but without their staying there. Thus, the geometries of the enclosure, the object array, and the discrete objects, together shape exploratory behavior in rats.

Traveling in the dark: the legibility of a regular and predictable structure of the environment extends beyond its borders.

The physical structure of the surrounding environment shapes the paths of progression, which in turn reflect the structure of the environment and the way that it shapes behavior. A regular and coherent physical structure results in paths that extend over the entire environment. In contrast, irregular structure results in traveling over a confined sector of the area. In this study, rats were tested in a dark arena in which half the area contained eight objects in a regular grid layout, and the other half contained eight objects in an irregular layout. In subsequent trials, a salient landmark was placed first within the irregular half, and then within the grid. We hypothesized that rats would favor travel in the area with regular order, but found that activity in the area with irregular object layout did not differ from activity in the area with grid layout, even when the irregular half included a salient landmark. Thus, the grid impact in one arena half extended to the other half and overshadowed the presumed impact of the salient landmark. This could be explained by mechanisms that control spatial behavior, such as grid cells and odometry. However, when objects were spaced irregularly over the entire arena, the salient landmark became dominant and the paths converged upon it, especially from objects with direct access to the salient landmark. Altogether, three environmental properties: (i) regular and predictable structure; (ii) salience of landmarks; and (iii) accessibility, hierarchically shape the paths of progression in a dark environment.

Network analysis of rat spatial cognition: behaviorally-established symmetry in a physically asymmetrical environment.

BACKGROUND: We set out to solve two inherent problems in the study of animal spatial cognition (i) What is a "place"?; and (ii) whether behaviors that are not revealed as differing by one methodology could be revealed as different when analyzed using a different approach. METHODOLOGY: We applied network analysis to scrutinize spatial behavior of rats tested in either a symmetrical or asymmetrical layout of 4, 8, or 12 objects placed along the perimeter of a round arena. We considered locations as the units of the network (nodes), and passes between locations as the links within the network. PRINCIPAL FINDINGS: While there were only minor activity differences between rats tested in the symmetrical or asymmetrical object layouts, network analysis revealed substantial differences. Viewing 'location' as a cluster of stopping coordinates, the key locations (large clusters of stopping coordinates) were at the objects in both layouts with 4 objects. However, in the asymmetrical layout with 4 objects, additional key locations were spaced by the rats between the objects, forming symmetry among the key locations. It was as if the rats had behaviorally imposed symmetry on the physically asymmetrical environment. Based on a previous finding that wayfinding is easier in symmetrical environments, we suggest that when the physical attributes of the environment were not symmetrical, the rats established a symmetric layout of key locations, thereby acquiring a more legible environment despite its complex physical structure. CONCLUSIONS AND SIGNIFICANCE: The present study adds a behavioral definition for "location", a term that so far has been mostly discussed according to its physical attributes or neurobiological correlates (e.g.--place and grid neurons). Moreover, network analysis enabled the assessment of the importance of a location, even when that location did not display any distinctive physical properties.

Arena geometry and path shape: when rats travel in straight or in circuitous paths?

We show here that the global geometry of the environment affects the shape of the paths of travel in rats. To examine this, individual rats were introduced into an unfamiliar arena. One group of rats (n=8) was tested in a square arena (2 m × 2 m), and the other group (n=8) in a round arena (2 m diameter). Testing was in a total darkness, since in the absence of visual information the geometry is not perceived immediately and the extraction of environment shape is slower. We found that while the level of the rats' activity did not seem to differ between both arenas, path shape differed significantly. When traveling along the perimeter, path shape basically followed the arena walls, with perimeter paths curving along the walls of the round arena, while being straight along the walls of the square arena. A similar impact of arena geometry was observed for travel away from the arena walls. Indeed, when the rats abandoned the arena walls to crosscut through the center of the arena, their center paths were circuitous in the round arena and relatively straight in the square arena. We suggest that the shapes of these paths are exploited for the same spatial task: returning back to a familiar location in the unsighted environment.

The dynamic process of cognitive mapping in the absence of visual cues: human data compared with animal studies.

The present study aimed to investigate the behavior involved in constructing spatial representation in humans. For this, blindfolded adult human subjects were introduced into an unfamiliar environment, where they were requested to move incessantly for 10 min. Analysis of the locomotor activity of the participants revealed the following exploratory behaviors: (1) ;looping'; (2) ;wall-following'; (3) ;step-counting'; (4) ;cross-cutting'; and (5) ;free traveling'. Looping is a typical exploratory mode of sightless explorers, based on returning to a recently traveled place. Wall-following is common in enclosed spaces, whereby explorers follow the perimeter of the environment. Both looping and wall-following are based on an egocentric frame of reference by which explorers obtain information about the shape, size and landmarks in the environment. Blindfolded explorers displayed step-counting in order to scale the environment and the relationships in it. Altogether, exploration by looping, wall-following and step-counting resulted in an allocentric spatial representation. The acquisition of spatial representation was manifested by cross-cutting and free travel, with subjects walking in a relatively fast and decisive manner. In light of the above modes of activity, we suggest that exploration of an unfamiliar environment is a synergetic self-organized process (synergetic inter-representation networks, SIRN model); an interplay between external and internal representations. According to this model, the interplay gives rise to an order parameter, such as the environment's dimensions or geometry, enabling progression to a subsequent exploratory behavior. This dynamic and sequential interplay reaches a steady state when a spatial representation (i.e. ;cognitive map') is established.

The impact of landmark properties in shaping exploration and navigation.

This study was aimed at uncovering physical and geometric properties that make a particular landmark a target of exploration and navigation. Rats were tested in a square open-field arena with additional portable corners featuring the same properties as the arena corners. It was found that the routes of progression converged upon the added corners, whether located at the arena wall or the arena center. Route convergence upon the added corners involved numerous visits to these corners. However, time spent at the added corners was relatively short compared with the arena corners, including that from which rats were introduced into the arena. There was no differential effect of testing rats in light or dark, or with a low versus a high portable corner. It is suggested that the added corners were distinct against the background of the arena enclosure, whereas the four arena corners and walls were encoded by the rats as one geometric module. This distinctness, together with the greater accessibility of the added corners, made them salient landmarks and a target of exploration. Thus, the impact of a landmark extended beyond its specific self-geometry to include accessibility and distinctness, which are contextual properties. In addition to the contextual impact on locomotor behavior there was also a temporal effect, with security initially dominating the rats' behavior but then declining along with an increased attraction to salient landmarks. These spatiotemporal patterns characterized behavior in both lit and dark arenas, indicating that distal cues were secondary to local proximal cues in shaping routes.